Television receivers having separate inputs for RF video sources, for auxiliary baseband composite video sources and for auxiliary component sources (e.g., SVHS) are known. To avoid picture flashing when switching between different sources (due to DC level differences) it is common to clamp the various sources of a common reference voltage level prior to switching. Subsequent processing of the selected video luminance component requires synchronizing signal separation and, typically, this also involves additional clamping to ensure proper operation of the sychnronizing signal separator.
FIG. 3 herein shows an example of such a separation circuit. As shown, the input clamps comprises a pair of capacitors 302 and 304 for coupling the luminance signals Y1 and Y2 to respective inputs of a video selection switch 312. A reference voltage source (shown as a battery) 310 is coupled to the switch inputs via a pair of, so-called, "sync-tip" clamp diodes 306 and 308 whereby the luminance input signals Y1 and Y2 are clamped to a sync tip level to about the potential of the reference. The syncronizing signal separator 314 includes a clamp 316 provided with a reference voltage by source 318. The reference voltage of source 318 is offset by another reference voltage 320. A comparator 322 compares the clamped video provided by clamp 316 with the offset reference voltage from source 320 to provide a separated composite synchronizing output signal.